Prior to feeding to a sewing machine, a pair of workpieces to be stitched together must be aligned and temporarily fastened to one another. The particular form of a clamp or a gripper for effecting this fastening is generally determined by the shapes or contours of the workpieces and by the nature of the stitching to be performed. Insofar as the workpieces are essentially regular in form and of substantially the same length and contour, a simple and generally servo-actuated clamp, such as that described in German utility patent (deutsche Gebrauchsmusterschrift) Ser. No. 1,961,860, is sufficient.
If the workpieces are irregular in form, it is necessary to utilize a gripper or fastening assembly including a multiplicity of individual clamps. German Open Application (deutsche Auglegeschrift) Ser. No. 2,164,862 described such a workpiece gripper assembly which is provided with shiftably mounted and commonly actuatable clamps.
To the state of the art also belongs a gripper assembly, according to German utility patent Ser. No. 1,982,797, in which one workpiece is laid over another and which is provided with a special device for putting pleats or folds into the workpieces.
In known positioning and fastening assemblies of the above-described type, it is generally difficult to position a second workpiece or fabric strip on a previously positioned and clamped strip, owing to catching of the strips and consequent ruffling of the upper strip. In addition, some workpieces are inherently difficult to position prior to clamping, e.g. because of a high density and/or a high flexibility.